Exhaust brake

ABSTRACT

An exhaust brake for an engine-driven vehicle responsive to engine vacuum for increasing exhaust back pressure and reducing engine vacuum during deceleration. An exhaust brake valve is operable to restrict exhaust fluid during braking and includes means for adjusting the exhaust back pressure. Exhaust fluid and engine vacuum are controllably supplied to close and open the exhaust brake valve in accordance with engine vacuum as sensed by an exhaust brake regulator. The exhaust brake regulator employs a vacuum actuated switch for initiating braking in response to a selected level of vacuum developed when the engine throttle is released. A latching circuit in the regulator maintains the brake until engine vacuum drops to a level indicating either that the engine throttle has been increasingly opened or that the engine is about to stall. During braking, the regulator vents the engine intake manifold to atmosphere.

United States Patent 191 King l l 1451 Oct. 1,1974

1 EXHAUST BRAKE [76] Inventor: Louis T. King, 2901 E. Pierson,

Phoenix, Ariz. 85016 [22] Filed: July 10, I972 [21] Appl. No.: 270,262

[52 U.S.'Cl. 1123/97 B [51]v Int. Cl. F02d 35/02 [58] Field of Search...; 123/97 B, 119 D [56] References Cited UNITED STATES PATENTS 1,667,016 4/1928 Stokes 123/97 B 2,168,232 8/1939 Messinger 123/97 B 2,220,686 11/1940 Oberhollenzer. 12-3/97 B 2,724,375 11/1955 Schaffer .1... 123/97 B 2,744,510 5/1956 Tyler et a1 123/97 B 2,767,697 9/1956 Udale 123/97 B 3,601,106 8/1971 Nakajima 123/119 D FOREIGN PATENTS OR APPLICATIONS 299,198 5/1912 .Germany mm B 71/ '2. H4 M1 k w w E //i- W 4 14 /f1 74/ w 'l /74 y;

f4 I 4% o Primary ExaminerCharles J. Myhre Assistant ExaminerW. Rutledge, .I r. Attorney, Agent, or Firm-Harness, Dickey & Pierce 5 7 ABSTRACT An exhaust brake for an engine driven vehicle responsive to engine vacuum for increasing exhaust back pressure and reducing engine vacuum during deceleration. An exhaust brake valve is operable to restrict exhaust fluid during braking and includes means for adjusting the exhaust back pressure. Exhaust fluid and engine vacuum are controllably supplied to close and open the exhaust brake valve in accordance with engine vacuum as sensed by an exhaust brake regulator. The exhaust brake regulator employs a vacuum actuated switch for initiating braking in response to a selected level of vacuum developed when the engine throttle is released A latching circuit in the regulator maintains the brake untiljerigine acuumarops to a level indicating either that the'engine'throttle has been increasingly opened or that the engine is about to stall. During braking, the regulator vents the engine intake manifold to atmosphere.

35 Claims, 5 Drawing Figures PMEMEMW H 3.838.670

- sum 1 er 3 v PAFEMIEMBI H874 3.838.670 sneer ear '3 EXHAUST BRAKE This invention relates to an exhaust brake particularly suited for an engine driven vehicle.

An important object of the present invention is 'to provide an exhaust brake automatically operable upon throttling down the engine and automatically releasable upon either subsequent throttling up or incipient stalling of the engine. Further objects'a're to reduce maintenance costs on: wheel brakes, spark plugs, piston rings and valves by reducing the severity with which these parts'are operated; and lubricant and fuel costs by minimizing engine oil pumping and gas consumption during deceleration.

2 Other significant aspects of the invention relate to improvements in the-exhaust brake regulator and the exhaust brake valve. The regulator is a compact'unit which can be readily mounted in virtually any engine compartment and connected to sense engine intake vacuum, representative of engine operating condition. The regulator quickly, reliably and accurately controls the exhaust brake valve in accordance with predetermined degrees of engine vacuum. The regulator also vents the intake manifold to atmosphere during breaking; this both reduces engine vacuum to a level which eliminates poor carburetion, excessive oil pumping, excessive fuel consumption and excessive air pollution, and also provides fluid which is drawn into the engine and compressed by the engine pistons to more efficiently brake the engine. Theexhaust brake valve is closed with theengine off but is opened by engine vac uum during engine starting, acceleration and cruising. Upon'throttle release, engine vacuum is removed from the exhaust brake valve and replaced by engine exhaust fluid which forces the valve to block the main flow path through the valve and develop'back pressure for braking the engine. An important feature of the exhaust brake valve is an adjustable by-pass restriction through which the engine exhaust fluid is forced when the main flow path through the valve is blocked. Adjustment of this restriction variesthe back pressure developed by the valve and hence, the braking torque developed to brake theengine.

The foregoing as well as additional objects, advantages and benefits of the invention will become apparent in the following description which isto be taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 2 is a semi-schematic cross-sectional view of the engine exhaust brake of the present invention and shown in the non-braking condition.

FIG. 3 is a view like FIG. 2 except shown during braking. FIG. 4'is an enlarged view of a portion of the exhaust 3 brake regulator shown in FIGS. 2 and 3.

FIG. 5 is a sectional view taken along line 5-5 in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 the engine exhaust brake of the present invention is connected with the engine system of the vehicle and comprises an exhaust brake valve 12, a solenoid-actuated selector valve l4 and an exhaust brake regulator 16. Brake valve 12 is connected in the engine exhaust line between pipes 18 and I8 and controls the exhaust flow from the engine exhaust manifold 20. When valve 12 is open, exhaust fluid can flow freely through the valve to atmosphere, but when closed. fluid flow is restricted so that increased back pressure is developed at exhaust manifold 20 to brake the engine. Selector valve 14 is connected to brake valve 12 by conduits 22 and 24 via which valve 12 is actuated to the open and closed positions.- A T-type conduit connection 26 connects selector valve 14 and regulator 16 with the engine intake manifold 28 so that engine vacuum is supplied to both valve l4 and regulator 16. Varv ious lead wires (not shown in FIG. 1) connect valve 14 to regulator 16 and regulator 16 to the vehicle battery (not shown). As will be apparent, exhaust brake 10 can be conveniently installedin a vehicle.

The details of exhaust brake 10 are shown in FIGS.

. 2 and 3. Brake valve 12 comprises a housing 30 having cle or the preference of the vehicle operator. A nut an inlet 32 and an outlet 34, pipe 18 being connected to inlet 32 and pipe 18 to outlet 34. The interior of housing 30 is hollow and forms an exhaust fluid passage through valve 12 between inlet 32 and outlet 34. An orifice 36 is disposed within housing 30 at the interior end of inlet 32, and a valve member 38 is movably mounted within housing 30 to open and close orifice 36 and respectively pass and block exhaust flow through the valve. Valve member 38 is mounted on a yoke 40 which is pivoted on housing .30 as at 42. Housing 30 is fashioned with a vertical cylindrical bore 44 above and between inlet 32 and outlet 34. A piston 46 is slidably arranged within bore 44. Piston 46 has a rod 48 projecting downwardly from the head 49 of piston 46, and a roller 50 on the lower end of rod 48 is captured within yoke 40. With this arrangement, when piston 46 moves up and down within bore 44, yoke 40 pivots valve 38 to open and close orifice 36. The open upper end of housing 30'above bore 44 is enclosed by a cover 52. A spring 54 is compressed between cover 52 and piston head 49 to bias piston 46 downwardly and forcibly urge valve member 38 against orifice 36. 1

In accordance with one of the inventive features, valve 12 is provided with an adjustable bypass restriction around-orifice 36. This bypass comprises intersecting passages 56 and 58 which intercept inlet 32 and the interior of housing 30 respectively. Housing 30 is formed with an external boss 60 aligned with passage 58. Boss 60 comprises a threaded bore 62 axially aligned with passage 58 but of a slightly greater diameter. A needle valve member 64 has a threaded body 66 threadedly engaging bore 62 and also a needle 68 on the inner end of body 66 which extends into passage 58. Member 64 can be advanced and retracted within bore 62 to move needle 68 into and out of passage 58 and thereby vary the restriction through the bypass.

This convenient adjustment allows the degree of engine braking provided by valve 12 to be set to any desired level in accordance with the requirements of the vehiis threaded onto the exterior end of body 68 and tightened against boss 60 to lock member 64 in its adjusted position. 7

Brake valve 12 further includes an exhaust fluid. passage 72 formed'as a continuation of passage 56 to communicate inlet 32 to conduit 24..An inlet passage '74 is formed in the center of cover 52 to communicate conduit 22 with bore 44 for actuating piston 46. Selector valve 14 comprises a housing 76 and ports 78, 80 and 82 formed in housing 76. Conduits 22 and 24 are connected to ports 80 and 78 respectively, while port 82 is connected via connection 26 to intake manifold 28. A movable valve member 84 is arranged within housing 76to alternately block ports 78 and 82. Valve member 84 is biased-downwardly by a compression spring 86 to block port 78 and open'port 82 thereby forming a fluid passage between ports 82 and 80. In this position, vacuum from intake manifold 28 can be supplied to inlet 74 of valve 12. A solenoid 88 within housing 76 is energizable to move .valve member 84 upwardly opening port 78 and blocking port 82 to form a fluid passage between port 78 and port 80. In this position, exhaust fluid from exhaust manifold can be supplied to inlet 74 of valve 12.

Valves 12 and 14 operate as follows. When the engine is cranked, vacuum developed in intake manifold 28 is transmitted through selector valve 14 to brake valve 12. The intensity of vacuum applied to piston 46 overcomes the downward force of spring 54,.and piston 46 moves upwardly within bore 44 to'open orifice 36.

Engine vacuum continues to be supplied to hold valve 12 open as the engine accelerates to a steady running or cruising speed; hence, engine exhaust freely passes through valve 12 as shown in FIG. 2..

. Upon release of the throttle, i.e., throttling down, so-

lenoid 88 is energized by regulator 16. (The operation of regulator 16 will be described later.) Port 82 is suddenly closed thereby trapping vacuum in bore 44 between piston 46 and cover 52, and simultaneously, the passage through selector valve 14 between ports 78 and 80 opens. The downward force on piston 46 is initially caused only by spring 54 and subsequently bypressure of the exhaust fluid in bore 44 as a re sult' of a rise in said pressure resulting from a moderate restriction caused by spring 54 partially closing valve member 38 on orifice 36. Orifice 36 becomes fully restricted and exhaust fluid is forced to flow through the restricted bypass circuit with the engine back'pressure developed by valve 12 increasing to a level determined by the adjustment setting of valve member 64. The over-running engine now acts as a compressor to discharge exhaust-fluid through the restricted bypass against the increased back pressure to thereby retard the speed of the vehicle. It will be apparent that needle valve member 64 provides an important and useful, yet simple and convenient, adjustment for varying the engine braking torque developed by the valve. The adjustment readily adapts the exhaust brake for different ivehicles and once installed on a given vehicle can thereafter be ad-.

justed whenever; it is desired to adjust the vehicle retarding force developed by the exhaust brake. .In a

modified form, provision could be made for the vehicle operator to remotely adjust the by-passrestriction from braking.

the cab of the vehicle to thereby control the amount of Selector valve 14 is de-energized by regulator 16 upon subsequent opening of the engine throttle (throt-. tling up) or an incipient stall condition. Upon de- The pressure fluid within bore 44 flows rapidly through valve 14 to intake manifold 28.and vacuum is rapidly developed in bore 44. Accordingly, piston 46 is operated to its upper position (HO. 2) holding valve 12 open so that exhaust fluid can flow freely from'pipe 18 to pipe 18.

An advantage of forcibly biasing valve member 38 to close orifice 36 is that when the engine is stopped. re verse circulation of cooler air through partially open engine exhaust valves, which mightwarp the valves. is prevented. Alternatively, it may be desirable to maintain valve member 38 partially open upon shutdown to prevent cold start problems.

Regulator 16 comprises a generally cylindrical housing "A horizontal passage 102 extends transversely through the lower end of housing 100. The right end of passage 102 is connected to'intake manifold 28 via conduit 26 and the left end has threadedly inserted therein -a vacuum-actuated electric switch 104. Switch 104 comprises a movable diaphragm 106 carrying a contact 108. A spring 110 biases diaphragm .106 to the left and this biases contact 108 out of engagement with fixed contacts 112 and 114 which are connected to extemal terminals 116 and 118 respectively. The right side of diaphragm 106 communicates via passage 102 and conduit 26 to intake manifold 28, and the left side to atmosphere. When engine vacuum reaches a preselected level relative to atmosphere, diaphragm 106 sufficiently compresses spring 110 to mate contact 108 pressure. It is contemplated that thisfeature would be desirable where the vehicle is operated at varying altitudes, as during running over mountainous terrain.

The upper end of housing 100 comprises a vertical cylindrical bore 120 extending downwardly from the upper end of housing 100 to an annular wall 122 extending around the interior of bore 120 just above passage 102. A cylindrical wall ,l24extends upwardly from v the inner'periphery of wall 122 approximately onefourth the length of bore 120 and forms a passage 125 intercepting passage 102.1The open upper end of bore 120 is enclosed by a cover 130. A piston 126 is slidably arranged within bore .120, and a compression spring 128 is disposed between cover 130 and piston 126 to bias the piston downwardly and close piston head 127 on the open upper end of passage 12S. Piston 126 includes a hollow stem 132 extending axially downwardly from the center of head 127. One or more openings 134 communicate the interior of stem 132 withpassage 102.

' A solenoid actuated valve 136 is coaxially mounted within bore 120 on cover 130. Valve 136 comprises a solenoid coil 138 and a central cylindrical sleeve 140 extending axially of bore 120 through .coil 138. A cupshaped member 142 is mounted on the lower end of coil 138 and includes a downwardly extending tubular sleeve 144 which is telescopically engaged with stem 132. A plurality of openings 146 extend through the end and side walls of member 142 to communicate the interior of member 142 with the bore space beteen piston 126 and cover 130. Member 142 is adapted to interengage piston head 127 for limiting upward travel of piston 126. Valve 136 further includes a movable valve member 148 operable to open and close the upper end of sleeve 144. Valve member 148 comprises a cylindrical shank 150 inserted into the open lower end of sleeve 140, and a head 152 on the lower end of shank 150. A compression spring153 disposed around shank 150 between the lower end of coil 138 and head 152 biases member 148 downwardly to close head 152 on sleeve 144. A stud 154 is affixed to the upper end of coil 138 and extends upwardly through cover 130. A central vent passage 156 extends completely through stud 154. An axially extending slot 158 in the side of shank 150 extends from the upper end of the shank to a level just above head 152. With valve member 148 closing sleeve 144 the interior of member 142 and the upper side of piston 126 are vented to atmosphere via passage 156 and slot 158. It will be noticed that the ra dially inner surface of slot 158 lies radially outwardly of vent passage 156. When coil 138 is energized, valve member 148 moves upwardly to open sleeve 144 and the upper end of shank 150 closes off the interior end of vent passage 156 so that the upper side of piston 126 is no longer vented to atmosphere.

Regulator 16 is preferably provided with its own air filter 160 and 'cover 162. Air filter 160 sits on a ledge 164 around housing 100 and cover 162 is secured by a wing nut 165 threaded onto stud 154. Housing 100 is provided with side wall openings 166 which intercept bore 120 at approximately the same level as the upper end of passage 125. Openings 166 are just below piston head 127 with piston 126 biased to its downward position (FIG. 2) to communicate the annular space 168 around wall 124 to atmosphere through air filter 160.

A normally closed switch 170 is mounted on the lower end of housing 100. Switch 170 comprises a fixed contact 172 and a movable contact 174 connected to terminals 176 and 178 respectively. A small deformable seal 180 covers a small circular hole in the bottom of housing 100 just above switch 170. When piston 126 is biased to its downward position, stem 132 deforms seal 180 disengaging contacts 172 and 174 via a plunger 184. As piston 126 moves upwardly, stem 132 releases plunger 184 so that contacts 172 and 174 close to complete a circuit between terminals 176, 178.

Switches 104 and 170, solenoid coils 88 and 138, and the vehicle battery are electrically connected as follows. A wire 190 connects terminals 1 16 and 178 to the positive battery terminal; a wire 192 connects terminals 176 and 118 to one terminal of each solenoid coil 88, 138 and a ground wire 194 connects the other terminal of each solenoid to the battery ground terminal.

Regulator 16 operates as follows. With the engine off, spring 128 biases piston 126 to close passage 125, and spring 153 biases valve member 148 to close sleeve 144. In this condition, the upper surface of piston 146 is vented to atmosphere via passage 156, slot 158 and orifices 146. The outer annular surface 198 on the lower side of piston head 127 directly above space 168 is vented to atmosphere via openings 166. The inner annular surface 200 on the lower side of piston head 127 between stem 132 and wall 124 communicates via passages 125 and 102 to intake manifold 28. Note that switches 104 and 108 are both open.

When the engine is cranked, vacuum developed in intake manifold 28 is transmitted to switch 104 and the annular piston surface 200. Since piston 126 is at its full downward position, the vacuum applied to piston surface 200 causes no additional piston displacement. The vacuum applied to switch 104 moves contact 108 to the right against the force of spring but not enough to complete the circuit between terminals 116 and 118. The engine vacuum during subsequent acceleration and cruising is insufficient to move piston 126 or close switch 104. a

When the engine throttle is released, for example to the idle position in FIG. 3, vacuum'in intake manifold 28 increases to a magnitude sufficient to close switch 104 and in turn energize coils 88 and 138. Energization of coil 88 operates valve 14 and in turn valve 12 to restrict engine exhaust as previously described. Energization of coil 138 moves valve member 148 upwardly to block vent 156 and open sleeve 144. The relatively high engine vacuum is conducted through stern 132, sleeve 144 and orifices 146 to be effective on the upper side of piston 126. Since piston surface 200 is communicated to atmosphere via openings 166, a net upward force is applied to piston 126 urging the piston upwardly against spring 128. As piston 126 unseats to open passage 125, air is drawn through openings 166 and rushes through passages and 102 toward intake manifold 28. Shortly afer a small preselected upward displacement of piston 126, stern 132 releases plunger 184 closing switch 170. With switch connected in parallel with switch 104 as illustrated, the closure of switch 170 is effective to seal solenoids 88 and 138. Thus as the air entering intake manifold 28 via regulator 16 decreases the engine vacuum to a level insufficient to hold switch 104 closed (as illustrated in FIG. 3), switch 170, having been closed by the unseating of piston 126, maintains coils 88 and 138 energized. The only way in which coils 88 and 138 can be deenergized is by subsequent operation of plunger 184 by stern 132 to open switch 170. Since valve member 148 is therefore kept open, engine vacuum is supplied to the upper side of piston 126 via stern 132. With piston 126 unseated, air'is drawn through regulator 16 to in-, take manifold 28 so that engine vacuum is reduced to a level which eliminates poor carburetion, excessive oil pumping, excessive fuel consumption and excessive air pollution. This vacuum level is approximately equal to that developed during normal cruising and acceleration. Moreover, this venting of manifold 28 to atmosphere allows the engine to intake and compress large fluid volumes thereby advantageously improving the braking capacity.

As the engine speed drops, engine vacuum decreases. This decrease is transmitted through stem 132 and sleeve 144 to the upper side of piston 126. When the vacuum drops to a preselected level representative of incipient engine stalling, the net upward force on piston 126 positions the piston to where the stem 132 opens switch 170. Upon opening of switch 170, coil 88 is deenergized to open brake valve 12 as above described, and coil 138 is de-energized to close passage 144 and to open passage 156 to in turn vent the upper side of piston 126 to atmosphere. Spring 128 now pushes pis-,

ton 126 closed on passage 125 to block air flow through regulator 16 to intake manifold 28. The engine throttle now regains control just in time to prevent the engine from stalling. Alternatively, opening theengine throttle during braking would also create a drop in engine vacuum sufficient to cause regulator 16 to close piston 126 on passage 125; hence, upon throttling up, regulator 16 allows the engine throttle to quickly regain control for accelerating the engine. Note: the level of engine vacuum to which regulator 16 is responsive may be varied in accordance with specific vehicle requirements; for example, on a vehicle equipped with vacuum boost for the wheel brakes,engine vacuum should be maintained at a level sufficient to permit the wheel brakes to be actuated, even if this level is somewhat above the level indicative of incipient engine stalling. Accordingly, it will be appreciated that reference to incipient engine stall can include conditions well in advance of actual stalling; hence, it may be desirable in some installations to use an available engine speed signal for de-energizing the system prior to stalling.

An additional feature which may be included is the provision of an optional switchto engage an additional circuit on vehicles with electrical switch operated passing gear in the automatic transmission. This downshiftcircuit is energized automatically whenever the exhaust brake system is energized to obtain a maximum amount of braking. This eliminates the need of the operator to manually downshift for maximum braking each time the automatic exhaust brake system comes on in mountainous or city driving. This system would preferably be used at speeds below 50 mph.

Since a large amount of the kinetic energy of the vehiclehas been dissipated by the exhaust brake, the wear on the wheel brakes is minimized. Moreover, by venting the intake manifold to atmosphere during braking, engine deposits on spark plugs, valves, etc. are minimized. Thus, the invention improves the overall operation of the vehicle and helps to minimize maintenance costs on wheel brakes, spark plugs, valves, etc.

While it will be apparent that the invention herein disclosed is well calculated to achieve the benefits and advantages as hereinabove set forth, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the spirit thereof.

I claimi I 1. In an engine-driven vehicle having an exhaust brake of the type wherein a brake valve is connected in the engine exhaust line and is operable to control.

signal whereby the brake valve is closed in response to said predetermined engine operating condition, said means operatively coupling said vacuum actuated switch means with the brake valve comprising a solenoid operable in response to said signal and means operatively coupling said solenoid with the brake valve such that the brake valve is closed inresponse to operation of said solenoid, said last-mentioned means com-.

prising a control valve means and a source of pressure fluid, said control valve means being operable in response to operation of said solenoid for causing pressure fluid to be conducted from said source .to said brake valve, said brake valve being closed in response to application of pressure fluid thereto, said source of pressure fluid being exhaust line fluid and said brake valve including an actuator conduit means communicating the engine exhaust line upstream of said brake valve to said actuator, said control valve means being disposed in said conduit means.

2. In an exhaust brake .for an engine having an airfuel mixture inlet and an exhaust fluid outlet, the combination comprising an exhaust brake valve for controlling the flow of exhaust fluid from the engine exhaust fluid outlet in accordance with engine operating conditions, said valve comprising an inlet adapted to be connected to the engine exhaust fluid outlet, an outlet. valving means movable between restricting and nonrestricting positions for controlling the flow of exhaust fluid through said valve between said valve inlet and said valve outlet, bias means for forcibly biasing said valving means toward the restricting position such that with the engine not running, said valving means is biased to the restricting position andcontrol means operative when the engine is running for overcomingthe bias imposed on said valving means by said bias means and causing the valving means to operate to the nonrestricting position so long as engine intake vacuum at the air-fuel mixture inlet does not exceed a predetermined magnitude but, when engine intake vacuum increases beyond said predetermined magnitude, said control means causes said valving means to operate to the restricting position.

3. The combination of claim 2 wherein said bias means comprises spring means.

4. .The combination of claim 2 wherein said control means comprises fluid actuated actuating means for operating said valving means between the restricting and non-restricting positions.

5. The combination of claim 4 wherein said fluid actuated actuating means comprises a fluid cylinder, said cylinder comprising a bore and a piston movable within said bore between first and second axial positions, means operatively coupling said piston with said valv- -ing means such that when said piston moves from the passage means being connected to said bore such that when said control valve means is operated to conduct engine vacuum to said bore said piston is operated to its second axial position.

8. The combination of claim 5 wherein said control means includes exhaust fluid passage means connecting said bore with said valve inlet, control valve means in said exhaust fluid passage means for controlling the conduction of exhaust fluid to said bore, said passage means being connected to said bore such that when said control valve means is operated to conduct exhaust fluid to said boresaid piston is operated to its first axial position.

9. The combination of claim wherein said control means includes vacuum passage means connecting said bore with the engine air-fuel mixture inlet, exhaust fluid passage means connecting said bore with said valve inlet and control valve means operatively associated with said two passage means for controlling the conduction of vacuum and exhaust fluid to said bore, said two passage means being connected to said bore such thatwhen said control valve means is operated to conduct engine vacuum to said bore, said piston is operated to its second axial position and when said control valve means is operated to conduct engine exhaust fluid to said bore, said piston is operated to its first axial position.

10. The combination of claim 4 wherein said control means includes vacuum passage means communicating said fluid actuated actuating means with the engine airfuel mixture inlet whereby engine vacuum may be conducted to said actuating means for operatingsaid valving means to the non-restricting position.

11. The combination of claim 10 wherein said control means includes control valve means in said vacuum passage means for controlling conduction of engine vacuum to said actuating means.

12. The combination of. claim 4 wherein said control meansincludes exhaust fluid passage means communicating said valve inlet with said actuating means whereby exhaust fluid may be conducted to said actuating means for operating said valving means to the restricting position.

. position whereby the air-fuel mixture inlet is vented to atmosphere to reduce vacuum therein while the exhaust brake is braking the engine.

l5.'In an exhaust brake for an engine having an airfuel mixture inlet and an exhaust fluid outlet, the combination comprising an exhaust brake valve for controlling the flow of exhaust fluid from the engine exhaust fluid outlet in accordance with engine operating conditions, said valve comprising an inlet adapted to be connected to the engine exhaust fluid outlet, an outlet, valving means movable between restricting and nonrestricting positions for controlling the flow of exhaust fluid through said valve between said valve inlet and said valve outlet, actuating means for actuating said valving means between the restricting and nonrestricting positions, means forming a vacuum passage fromthe air-fuel mixture inlet to said actuating means, means forming an exhaust fluid passage from said valve inlet to said actuating means and control valve means for controlling the application of vacuum and exhaust fluid to said actuating means such that said valving means is operated to one of its positions when vacuum is supplied to said actuating means and to the other of its positions when exhaust fluid is supplied to said actuating means. I

'1 6. The combination of claim 15 wherein said actuating means comprises means for actuating said valving means to the non-restricting position when vacuum is supplied to said actuating means and means for operating said valving means to the restricting position when pressure fluid is supplied to said actuating means.

17. For an internal combustion engine having an airfuel mixture inlet and an exhaust line, an exhaust brake valve adapted to be connected in the exhaust line for controlling engine back pressure, said exhaust brake valve comprising in combination means forming an exhaust fluid passage through the valve, a valving member within said passage and movable between restrict ing and nomrestri'cting positions to control flow through said passage, means operatively coupling said valving member with said air-fuel mixture inlet such that said valving member is controllably operated in response to engine vacuum developed at saidair-fuel mixture inlet, and means forming a restricted passage shunting said valving member toprovide a shunt path for engine exhaust through the valve which is independent of the engine back pressure.

18. The combination of claim 17 including adjustment means for adjusting the restriction of said re stricted passage.

19. The combination of claim 18 wherein said adjustment means comprises a needle valve. 7 20. The engine exhaust brake of claim 17 wherein said exhaust brake valve includes a housing containing said valving member, said means forming said restricted passage shunting said valving member being providedin said housing.

21. An engine exhaust brake for connection in the exhaust line of an engine comprising a valving member operable between restricting and non-restricting positions for controlling the'flow of exhaust fluid from the engine to thereby control the back pressure applied to the engine, actuating means for operating said valving member from the non-restricting position to the restricting position in response to application of pressure fluid to said actuating means, conduit means communicating the engine exhaust line upstream of said valving member to said actuating means, and control means operable in response to a predetermined engine operatsaid control means is disposed in said conduit means.

, 23. The engine exhaust brake of claim 22 further including means for communicating engine manifold vacuum to said actuating means for causing said actuating means to operate said valving member to the nonrestricting position.

24. The engine exhaust brake of claim 21 further including bias means for biasing said valving member toward the restricting position when the engine is not running.

25. In an exhaust brake for an engine having an airfuel mixture inlet and an exhaust fluid outlet, the combination comprising an exhaust brake valve for controlling the flow of exhaust fluid from the engine exhaust fluid outlet in accordance with engine operating conditions, said valve comprising an inlet adapted to be connected to the engine exhaust fluid outlet, an outlet, valving means movable between restricting and nonrestricting positions for controlling the flow of exhaust fluid through said valve between said valve inlet and said valve outlet, said valving means being normally biased toward the restricting position with the engine not running and control means operative when the engine is running for overcoming the bias imposed on said valving meansand causing the valving means to operate to the non-restricting position so long as engine intake vacuum at the air-fuel mixture inlet does not exceed a predetermined magnitude but, when engine intake vacuum increases beyond said predetermined magnitude, said control means causes said valving means to operate to the restricting position.

26. In an exhaust brake for an engine having an airfuel mixture inlet and an exhaust fluid outlet, the combination comprising an exhaust brake valve for controlling the flow of exhaust fluid from the engine exhaust fluid outlet in accordance with engine operating conditions, said valve comprising an inlet adapted to be connected to the engine exhaust fluid outlet, an outlet, valving means movable between restricting and nonrestricting positions for controlling the flow of exhaust fluid through said valve between said valve inlet and said valve outlet, actuating means comprising fluid actuated means for actuating said valving means between the restricting and non-restricting positions and bias means comprising spring means for forcibly biasing .said valving means toward the restricting position, vacuum passage means communicating said fluid actuated actuating means with the engine air-fuel mixture inlet whereby engine vacuum may be conducted to said actuating means for operating said valving means; and control valve means in said vacuum passage means for controlling conduction of engine vacuum to said actu ating means, said actuating means comprising means responsive to application of vacuum to said actuating means bysaid control valve means for moving said valving means to the non-restricting position.

27. The combination of claim 26 including exhaust fluid passage, means communicating said valve inlet with said actuating means and additional control valve means in said exhaust fluid passage means for controlling the conduction of exhaust fluid to said actuating means whereby exhaust fluid may be conducted to said actuating means for operating said valving means.

28. The combination of claim 27 wherein said firstnamed control valve means and said additional control valve means are operable in unison such that exhaust fluid and engine vacuum are selectively'individually applied to said actuating means. v

29. The combination of claim 27 wherein said actuating means is-arranged to operate said valving means to the restricting position in response to conduction of exhaust fluid to said actuating means.

30. In an exhaust brake for an engine having an airfuel mixture inlet and an exhaust fluid outlet, the combination comprising an exhaust brake valve for controlling the flow of exhaust fluid from the engine exhaust restricting positions for controlling the flow of exhaust fluid through said valve between said valve inlet and said valve outlet, actuating means comprising fluid actuating means for actuating said valving means between the restricting and non-restricting positions and bias means comprising spring means for forcibly biasing said valving means toward the restricting position and exhaust fluid passage means communicating said valve inlet with said actuating means whereby exhaust fluid may be conducted to said actuating means for operating said valving means. I

31. The combination of claim 30 including control valve means in said exhaust fluid passage means for controlling conduction of exhaust fluid to said actuating means.

32. The combination of claim 31 wherein said actuating means comprises means responsive to application of exhaust fluid to said actuating means by said control valve means for moving said valving means to the restricting position.

' 33. In an exhaust brake for an engine having an airfuel mixture inlet and an exhaust fluid outlet, the combination comprising an exhaust brake valve for controlling the flow of exhaust fluid from the engine exhaust fluid outlet in accordance with engine operating conditions, said valve comprising an inlet adapted to be con nected to the engine exhaust fluid outlet, an outlet, valving means movable between restricting and nonrestricting positions for controlling the flow of exhaust fluid through said valve between said valve inlet and said valve outlet, actuating means comprising fluid actuating means for actuating said valving means between the restricting and non-restricting positions and bias means comprising spring means for forcibly biasing said valving means toward the restricting position, said fluid actuated actuating means comprising a fluid cylinder, said cylinder comprising a bore and a piston movable within said bore between first and second axial positions, means operatively coupling said piston with said valving means such that when said piston moves 'from the first position to the second position said valving means moves from the restricting position to the non-restricting position, said actuating means comprising vacuum passage means connecting said bore with the engine air-fuel mixture inlet,.and control valve means in said vacuum passage means for controlling conduction of engine vacuum to said bore, said passage means being connected to said bore such that when said control valve means is operated to conduct engine vacuum to said bore said piston is operated to its second axial position.

34. In an exhaust brake for an engine having an air fuel mixture inlet and an exhaust fluid outlet, the combination comprising an exhaust brake valve for controlling the flow of exhaust fluid from the engine exhaust 'der, said cylinder comprising a bore and a piston movable within said bore between first and second axial po- 13 v sitions, means operatively coupling said piston with said valving means such that when said piston moves from the first position to the second position said valving means moves from the restricting position to the non-restricting position, said actuating means comprising exhaust fluid passage means connecting said bore with said valve inlet, control valve means in said exhaust fluid-passage means for controlling the conduction of exhaust fluid to said bore, said passage means being connected to said bore such that when said control valve means is operated to conduct exhaust fluid to said bore said piston is operated to its first axial position.

35. In an exhaust brake for an engine having an airfuel mixture inlet and an exhaust fluid outlet, the combination comprising an exhaust brake valve for controlling the flow of exhaust fluid from the engine exhaust I fluid outlet in accordance with engine operating condisaid valve outlet, actuating means comprising fluid ac-- tuating means for actuating said valving means between the restricting and non-restricting positions and bias means comprising spring means for forcibly biasing said valving means toward the restricting position, said fluid actuated actuating means comprising a fluid cylinder, said cylinder comprising a bore and a piston mov- Y able within said bore between first and second axial positions, means operatively coupling said piston with said valving means such that when said piston moves from the first position to the second position said valving means moves from the restricting position to the non-restricting position, said actuating means comprising vacuum passage means connecting said bore with the engine air-fuel mixture inlet, exhaust fluid passage means connecting said bore with said valve inlet and control valve means operatively associated with said two passage means for controlling the conduction of vacuum and exhaust fluid to said bore, said two passage means being connected to said bore such that when said control valve means is operated to conduct engine vacuum to said bore, said piston is operated to its second axial position and when said control valve means is operated to conduct engine exhaust fluid to said 

1. In an engine-driven vehicle having an exhaust brake of the type wherein a brake valve is connected in the engine exhaust line and is operable to control fluid flow therethrough the combination comprising a vacuum actuated switch means actuable to provide a signal, means operatively coupling said vacuum actuated switch means with the engine air-fuel mixture inlet such that said vacuum actuated switch means is actuated by a preselected magnitude of engine vacuum developed at the air-fuel mixture inlet and representative of a predetermined engine operating condition to provide said signal and means operatively coupling said vacuum actuated switch means with said brake valve such that the brake valve is closed in response to said signal whereby the brake valve is closed in response to said predetermined engine operating condition, said means operatively coupling said vacuum actuated switch means with the brake valve comprising a solenoid operable in response to said signal and means operatively coupling said solenoid with the brake valve such that the brake valve is closed in response to operation of said solenoid, said last-mentioned means comprising a control valve means and a source of pressure fluid, said control valve means being operable in response to operation of said solenoid for causing pressure fluid to be conducted from said source to said brake valve, said brake valve being closed in response to application of pressure fluid thereto, said source of pressure fluid being exhaust line fluid and said brake valve including an actuator conduit means communicating the engine exhaust line upstream of said brake valve to said actuator, said control valve means being disposed in said conduit means.
 2. In an exhaust brake for an engine having an air-fuel mixture inlet and an exhaust fluid outlet, the combination comprising an exhaust brake valve for controlling the flow of exhaust fluid from the engine exhaust fluid outlet in accordance with engine operating conditions, said valve comprising an inlet adapted to be connected to the engine exhaust fluid outlet, an outlet, valving means movable between restricting and non-restricting positions for controlling the flow of exhaust fluid through said valve between said valve inlet and said valve outlet, bias means for forcibly biasing said valving means toward the restricting position such that with the engine not running, said valving means is biased to the restricting position and control means operative when the engine is running for overcoming the bias imposed on said valving means by said bias means and causing the valving means to operate to the non-restricting position so long as engine intake vacuum at the air-fuel mixture inlet does not exceed a predetermined magnitude but, when engine intake vacuum increases beyond said predetermined magnitude, said control means causes said valving means to operate to the restricting position.
 3. The combination of claim 2 wherein said bias means comprises spring means.
 4. The combination of claim 2 wherein said control means comprises fluid actuated actuating means for operating said valving means between the restricting and non-restricting positions.
 5. The combination of claim 4 wherein said fluid actuated actuating means comprises a fluid cylinder, said cylinder comprising a bore and a piston movable within said bore between first and second axial positions, means operatively coupling said piston with said valving means such that when said piston moves from the first position to the second position said valving means moves from the restricting position to the non-restricting position.
 6. The combination of claim 5 wherein said spring means comprises a spring biasing said piston toward the first axial position.
 7. The combination of claim 5 wherein said control means includes vacuum passage means connecting said bore with the engine air-fuel mixture inlet, control valve means in said vacuum passage means for controlling conduction of engine vacuum to said bore, said passage means being connected to said bore such that when said control valve means is operated to conduct engine vacuum to said bore said piston is operated to its second axial position.
 8. The combination of claim 5 wherein said control means includes exhaust fluid passage means connecting said bore with said valve inlet, control valve means in said exhaust fluid passage means for controlling the conduction of exhaust fluid to said bore, said passage means being connected to said bore such that when said control valve means is operated to conduct exhaust fluid to said bore said piston is operated to its first axial position.
 9. The combination of claim 5 wherein said control means includes vacuum passage means connecting said bore with the engine air-fuel mixture inlet, exhaust fluid passage means connecting said bore with said valve inlet and control valve means operatively associated with said two passage means for controlling the conduction of vacuum and exhaust fluid to said bore, said two passage means being connected to said bore such that when said control valve means is operated to conduct engine vacuum to said bore, said piston is operated to its second axial position and when said control valve means is operated to conduct engine exhaust fluid to said bore, said piston is operated to its first axial position.
 10. The combination of claim 4 wherein said control means includes vacuum passage means communicating said fluid actuated actuating means with the engine air-fuel mixture inlet whereby engine vacuum may be conducted to said actuating means for operating said valving means to the non-restricting position.
 11. The combination of claim 10 wherein said control means includes control valve means in said vacuum passage means for controlling conduction of engine vacuum to said actuating means.
 12. The combination of claim 4 wherein said control means includes exhaust fluid passage means communicating said valve inlet with said actuating means whereby exhaust fluid may be conducted to said actuating means for operating said valving means to the restricting position.
 13. The combination of claim 12 wherein said control means includes a control valve means in said exhaust fluid passage means for controlling conduction of exhaust fluid to said actuating means.
 14. The combination of claim 2 further including vent passage means communicating the engine air-fuel mixture inlet to atmosphere, vent valve means in said vent passage means for controllably venting the engine air-fuel mixture inlet to atmosphere, said control means including means for opening said vent valve means during operation of said valving means to the restricting position whereby the air-fuel mixture inlet is vented to atmosphere to reduce vacuum therein while the exhaust brake is braking the engine.
 15. In an exhaust brake for an engine having an air-fuel mixture inlet and an exhaust fluid outlet, the combination comprising an exhaust brake valve for controlling the flow of exhaust fluid from the engine exhaust fluid outlet in accordance with engine operating conditions, said valve comprising an inlet adapted to be connected to the engine exhaust fluid outlet, an outlet, valving means movable between restricting and non-restricting positions for controlling the flow of exhaust fluid through said valve between said valve inlet and said valve outlet, actuating means for actuating said valving means between the restricting and non-restricting positions, means forming a vacuum passage from the air-fuel mixture inlet to said actuating means, means forming an exhaust fluid passage from said valve inlet to said actuating means and control valve means for controlling the application of vacuum and exhaust fluid to said acTuating means such that said valving means is operated to one of its positions when vacuum is supplied to said actuating means and to the other of its positions when exhaust fluid is supplied to said actuating means.
 16. The combination of claim 15 wherein said actuating means comprises means for actuating said valving means to the non-restricting position when vacuum is supplied to said actuating means and means for operating said valving means to the restricting position when pressure fluid is supplied to said actuating means.
 17. For an internal combustion engine having an air-fuel mixture inlet and an exhaust line, an exhaust brake valve adapted to be connected in the exhaust line for controlling engine back pressure, said exhaust brake valve comprising in combination means forming an exhaust fluid passage through the valve, a valving member within said passage and movable between restricting and non-restricting positions to control flow through said passage, means operatively coupling said valving member with said air-fuel mixture inlet such that said valving member is controllably operated in response to engine vacuum developed at said air-fuel mixture inlet, and means forming a restricted passage shunting said valving member to provide a shunt path for engine exhaust through the valve which is independent of the engine back pressure.
 18. The combination of claim 17 including adjustment means for adjusting the restriction of said restricted passage.
 19. The combination of claim 18 wherein said adjustment means comprises a needle valve.
 20. The engine exhaust brake of claim 17 wherein said exhaust brake valve includes a housing containing said valving member, said means forming said restricted passage shunting said valving member being provided in said housing.
 21. An engine exhaust brake for connection in the exhaust line of an engine comprising a valving member operable between restricting and non-restricting positions for controlling the flow of exhaust fluid from the engine to thereby control the back pressure applied to the engine, actuating means for operating said valving member from the non-restricting position to the restricting position in response to application of pressure fluid to said actuating means, conduit means communicating the engine exhaust line upstream of said valving member to said actuating means, and control means operable in response to a predetermined engine operating condition to cause engine exhaust fluid to be supplied through said conduit means to said acutating means and thereby operate said valving member to the restricting position.
 22. The engine exhaust brake of claim 21 wherein said control means is disposed in said conduit means.
 23. The engine exhaust brake of claim 22 further including means for communicating engine manifold vacuum to said actuating means for causing said actuating means to operate said valving member to the non-restricting position.
 24. The engine exhaust brake of claim 21 further including bias means for biasing said valving member toward the restricting position when the engine is not running.
 25. In an exhaust brake for an engine having an air-fuel mixture inlet and an exhaust fluid outlet, the combination comprising an exhaust brake valve for controlling the flow of exhaust fluid from the engine exhaust fluid outlet in accordance with engine operating conditions, said valve comprising an inlet adapted to be connected to the engine exhaust fluid outlet, an outlet, valving means movable between restricting and non-restricting positions for controlling the flow of exhaust fluid through said valve between said valve inlet and said valve outlet, said valving means being normally biased toward the restricting position with the engine not running and control means operative when the engine is running for overcoming the bias imposed on said valving means and causing the valving means to operate to the non-restricting position so long as engine intake vacuum aT the air-fuel mixture inlet does not exceed a predetermined magnitude but, when engine intake vacuum increases beyond said predetermined magnitude, said control means causes said valving means to operate to the restricting position.
 26. In an exhaust brake for an engine having an air-fuel mixture inlet and an exhaust fluid outlet, the combination comprising an exhaust brake valve for controlling the flow of exhaust fluid from the engine exhaust fluid outlet in accordance with engine operating conditions, said valve comprising an inlet adapted to be connected to the engine exhaust fluid outlet, an outlet, valving means movable between restricting and non-restricting positions for controlling the flow of exhaust fluid through said valve between said valve inlet and said valve outlet, actuating means comprising fluid actuated means for actuating said valving means between the restricting and non-restricting positions and bias means comprising spring means for forcibly biasing said valving means toward the restricting position, vacuum passage means communicating said fluid actuated actuating means with the engine air-fuel mixture inlet whereby engine vacuum may be conducted to said actuating means for operating said valving means, and control valve means in said vacuum passage means for controlling conduction of engine vacuum to said actuating means, said actuating means comprising means responsive to application of vacuum to said actuating means by said control valve means for moving said valving means to the non-restricting position.
 27. The combination of claim 26 including exhaust fluid passage means communicating said valve inlet with said actuating means and additional control valve means in said exhaust fluid passage means for controlling the conduction of exhaust fluid to said actuating means whereby exhaust fluid may be conducted to said actuating means for operating said valving means.
 28. The combination of claim 27 wherein said first-named control valve means and said additional control valve means are operable in unison such that exhaust fluid and engine vacuum are selectively individually applied to said actuating means.
 29. The combination of claim 27 wherein said actuating means is arranged to operate said valving means to the restricting position in response to conduction of exhaust fluid to said actuating means.
 30. In an exhaust brake for an engine having an air-fuel mixture inlet and an exhaust fluid outlet, the combination comprising an exhaust brake valve for controlling the flow of exhaust fluid from the engine exhaust fluid outlet in accordance with engine operating conditions, said valve comprising an inlet adapted to be connected to the engine exhaust fluid outlet, an outlet, valving means movable between restricting and non-restricting positions for controlling the flow of exhaust fluid through said valve between said valve inlet and said valve outlet, actuating means comprising fluid actuating means for actuating said valving means between the restricting and non-restricting positions and bias means comprising spring means for forcibly biasing said valving means toward the restricting position and exhaust fluid passage means communicating said valve inlet with said actuating means whereby exhaust fluid may be conducted to said actuating means for operating said valving means.
 31. The combination of claim 30 including control valve means in said exhaust fluid passage means for controlling conduction of exhaust fluid to said actuating means.
 32. The combination of claim 31 wherein said actuating means comprises means responsive to application of exhaust fluid to said actuating means by said control valve means for moving said valving means to the restricting position.
 33. In an exhaust brake for an engine having an air-fuel mixture inlet and an exhaust fluid outlet, the combination comprising an exhaust brake valve for controlling the flow of exhaust fluid from the engine exhaust fluid outlet in accorDance with engine operating conditions, said valve comprising an inlet adapted to be connected to the engine exhaust fluid outlet, an outlet, valving means movable between restricting and non-restricting positions for controlling the flow of exhaust fluid through said valve between said valve inlet and said valve outlet, actuating means comprising fluid actuating means for actuating said valving means between the restricting and non-restricting positions and bias means comprising spring means for forcibly biasing said valving means toward the restricting position, said fluid actuated actuating means comprising a fluid cylinder, said cylinder comprising a bore and a piston movable within said bore between first and second axial positions, means operatively coupling said piston with said valving means such that when said piston moves from the first position to the second position said valving means moves from the restricting position to the non-restricting position, said actuating means comprising vacuum passage means connecting said bore with the engine air-fuel mixture inlet, and control valve means in said vacuum passage means for controlling conduction of engine vacuum to said bore, said passage means being connected to said bore such that when said control valve means is operated to conduct engine vacuum to said bore said piston is operated to its second axial position.
 34. In an exhaust brake for an engine having an air-fuel mixture inlet and an exhaust fluid outlet, the combination comprising an exhaust brake valve for controlling the flow of exhaust fluid from the engine exhaust fluid outlet in accordance with engine operating conditions, said valve comprising an inlet adapted to be connected to the engine exhaust fluid outlet, an outlet, valving means movable between restricting and non-restricting positions for controlling the flow of exhaust fluid through said valve between said valve inlet and said valve outlet, actuating means comprising fluid actuating means for actuating said valving means between the restricting and non-restricting positions and bias means comprising spring means for forcibly biasing said valving means toward the restricting position, said fluid actuated actuating means comprising a fluid cylinder, said cylinder comprising a bore and a piston movable within said bore between first and second axial positions, means operatively coupling said piston with said valving means such that when said piston moves from the first position to the second position said valving means moves from the restricting position to the non-restricting position, said actuating means comprising exhaust fluid passage means connecting said bore with said valve inlet, control valve means in said exhaust fluid-passage means for controlling the conduction of exhaust fluid to said bore, said passage means being connected to said bore such that when said control valve means is operated to conduct exhaust fluid to said bore said piston is operated to its first axial position.
 35. In an exhaust brake for an engine having an air-fuel mixture inlet and an exhaust fluid outlet, the combination comprising an exhaust brake valve for controlling the flow of exhaust fluid from the engine exhaust fluid outlet in accordance with engine operating conditions, said valve comprising an inlet adapted to be connected to the engine exhaust fluid outlet, an outlet, valving means movable between restricting and non-restricting positions for controlling the flow of exhaust fluid through said valve between said valve inlet and said valve outlet, actuating means comprising fluid actuating means for actuating said valving means between the restricting and non-restricting positions and bias means comprising spring means for forcibly biasing said valving means toward the restricting position, said fluid actuated actuating means comprising a fluid cylinder, said cylinder comprising a bore and a piston movable within said bore between first and second axial positions, means operatively coupling said piston with said valving means such that when said piston moves from the first position to the second position said valving means moves from the restricting position to the non-restricting position, said actuating means comprising vacuum passage means connecting said bore with the engine air-fuel mixture inlet, exhaust fluid passage means connecting said bore with said valve inlet and control valve means operatively associated with said two passage means for controlling the conduction of vacuum and exhaust fluid to said bore, said two passage means being connected to said bore such that when said control valve means is operated to conduct engine vacuum to said bore, said piston is operated to its second axial position and when said control valve means is operated to conduct engine exhaust fluid to said bore, said piston is operated to its first axial position. 